1. Technical Field
The present invention relates generally to fuel control systems and, more particularly, to a method of controlling combustion parameters of an internal combustion engine in a motor vehicle capable of operating on more than one type of fuel.
2. Discussion
Environmental and energy independence concerns have stimulated the development of alternative transportation fuels, such as alcohol fuels, for use in automobiles. Alcohol fuels include methanol and ethanol. A flexible fueled vehicle capable of operating on gasoline, or alcohol fuel, or any mixture of the two fuels, is therefore in demand. Modifications to the engine are necessary when operating on different fuels because of the different characteristics of each fuel. For example, an engine operating on ethanol or E85 (a blend of 85% ethanol and 15% gasoline) requires approximately 1.4 times the amount of fuel relative to gasoline at stoichiometry due to a lower energy content of the ethanol.
Air/fuel ratio in internal combustion engine design is typically considered to be the ratio of mass flow rate of air to mass flow rate of fuel inducted by an internal combustion engine to achieve conversion of the fuel into completely oxidized products. The chemically correct ratio corresponding to complete oxidation of the products is called stoichiometric. If the air/fuel ratio is less than stoichiometric, an engine is said to be operating rich, i.e., too much fuel is being supplied in proportion to the amount of air to achieve perfect combustion. Likewise, if the air/fuel ratio is greater than stoichiometric, an engine is said to be operating lean, i.e., too much air is being supplied in proportion to the amount of fuel to achieve perfect combustion. Alcohol fuels have a lower air/fuel ratio than gasoline at stoichiometric, so that the engine must be compensated for in the rich direction as the percentage of alcohol in the fuel increases.
When the engine is operating in wide-open throttle or part throttle enrichment conditions, the fuel system is not in an oxygen feedback closed loop mode. In these conditions, the engine operates in a rich of stoichiometric air/fuel ratio. Previously, there was no method to update the alcohol fuel concentration value during open loop wide open throttle and part throttle enrichment operating conditions.
Therefore, it would be desirable to provide a feedback system to ensure a rich of stoichiometric air/fuel ratio for system durability at wide open throttle and part throttle enrichment conditions.